Understanding how epithelial sheets move and what controls their movements is fundamental for understanding a range of important normal and disease- related biological processes. A common feature of large-scale epithelial morphogenetic movements is that cells must undergo rearrangement while maintaining their integrity as an epithelium. As they do so, they must modulate their contact with the extracellular matrix and one another. Examples include th elongation and folding of the neural plate during neurulation, enlargement of the vertebrate forebrain, and the closure of wounds in embryonic epidermal tissue and adult epithelial tissues. Using the sea urchin gastrula as a model system, this proposal has the following four specific aims: (1) Analysis of specific motile behavior(s) exhibited by epithelial cells known to undergo rearrangement. Using computer-assisted videomicroscopy, time-lapse laser scanning confocal microscopy, and two-photon excitation confocal microscopy, we will test the hypothesis that basolateral protrusive activity mediates cell rearrangements in a temporally and spatially-specific manner. (2) Analysis of intrinsic and extrinsic mechanisms during cell rearrangement. Using microsurgery and laser ablation of specific cell populations, we will test the hypothesis that directional cell rearrangement can occur by two separate mechanisms _ active rearrangement, and passive rearrangement due to externally applied forces. (3) Analysis of the role of the apical extracellular matrix in mediating cell rearrangement. Using a variety of blocking agents, we will test the hypothesis that rearranging cells require attachment to the apical extracellular matrix. Blocking agents will include perturbing antibodies and recombinant competitive peptide inhibitors. (4) Analysis of the role of the basal lamina in mediating cell rearrangement. Using a 4.3 kB clone of the sea urchin laminin B1 chain and a 1.2 kB clone of the G domain of the sea urchin laminin A chain, we will generate antibody and competitive peptide reagents which will be used to test the hypothesis that basolateral motility during cell rearrangement requires attachment of the basolateral surfaces of rearranging cells to laminin. As a result of these studies, we believe that we will gain a better understanding of how the motility of individual cells contributes to successful epithelial cell rearrangement, as well as how aberrant motility contributes to failures in this ubiquitous morphogenetic process.